Hi there @eeeyanjan, Hello, in regards to your issue with Pokemon Go, there are several ways to solve the problem.
#1 Ensure that your GPS is activated on your phone and running in the background.
Open Google maps and make sure that it is able to detect locations. Pokemon Go is unable to detect your location without this feature activated. By keeping Google Maps active in the background it helps Pokemon Go obtain your location.
#2 Turn off Mock Locations-
Go to Settings and click “About Device”
You will see “Build Number” listed
Tap “Build Number” seven times and “Developer Options” will be activated
In the “Developer Actions” you will find “Mock Locations”
Disable “Mock Locations”
Return back to the main screen and start Pokemon Go again. The error should be gone and you can continue your hunt for Pokemon!
Honorable mention: Consider downloading an “GPS booster” application from the Play store to increase the GPS efficiency while you are out catching Pokemon.
Here's a video to show you how, whether using Android or iOS (iPhone)